1. Field of the Invention
The present invention relates to a thermokeratoplastic probe that is placed into direct contact with the outer surface of the cornea.
2. Description of Related Art
Techniques for correcting vision have included reshaping the cornea of the eye. For example, myopic conditions can be corrected by cutting a number of small incisions in the corneal membrane. The incisions allow the corneal membrane to relax and increase the radius of the cornea. The incisions are typically created with either a laser or a precision knife. The procedure for creating incisions to correct myopic defects is commonly referred to as radial kerectotomy and is well known in the art.
The techniques of radial kerectotomy are only effective in correcting myopia. Radial kerectotomy cannot be used to correct a eye condition such as hyperopia. Additionally, kerectotomy has limited use in reducing or correcting an astigmatism. The cornea of a patient with hyperopia is relatively flat. A flat cornea creates a lens system which does not direct the focal point of the viewed image to the optic nerve of the eye. Hyperopia can be corrected by reshaping the eye to decrease the radius of cornea. It has been found that hyperopia can be corrected by heating and denaturing local regions of the corneal membrane layer. The denatured tissue contracts the cornea and changes the shape of the eye. The procedure of heating the corneal membrane to correct a patient's vision is commonly referred to as thermokeratoplasty.
U.S. Pat. Nos. 4,461,294 issued to Baron; 4,976,709 issued to Sand and PCT Publication WO 90/12618, all disclose thermokeratoplastic techniques which utilize a laser to heat the corneal membrane. Although effective in reshaping the eye, the laser based systems of the Baron, Sand and PCT references are relatively expensive to produce. Expensive laser systems increase the cost of the procedure and are economically impractical for doctors with limited financial resources.
U.S. Pat. Nos. 4,326,529 and 4,381,007 issued to Doss disclose electrodes that are used to heat the corneal membrane of an eye. The electrode is located within a housing that spaces the tip of the electrode from the surface of the eye. An isotropic saline solution is irrigated through the electrode and aspirated through a channel formed between the outer surface of the electrode and the inner surface of the sleeve. The saline solution provides an electrically conductive medium between the electrode and the corneal membrane. The current from the electrode heats the outer layers of the eye. Subsequent cooling of the heated outer eye tissue causes the cornea to shrink to a new radial shape. The saline solution also functions as a coolant which cools the outer epithelium layer, so that the corneal membrane has a more uniform temperature gradient across the thickness of the eye.
The saline solution of the Doss device spreads the current of the electrode over a relatively large area of the cornea. Consequently, thermokeratoplasty techniques using the Doss device are limited to reshaped corneas with relatively large denatured areas. It is desirable to provide an electrode which can locally heat very small areas of the cornea. An electrode that creates relatively small heated areas would allow more flexibility in reshaping the cornea. This is particularly true if thermokeratoplasty is used to correct astigmatic conditions. It would therefore be desirable to have a thermokeratoplastic electrode which will allow the surgeon to heat relatively small areas of a corneal membrane.